The FCC process is well known and widely used to convert heavy feeds to lighter products. In the early days of FCC, more than 50 years ago, refineries processed distilled feeds over amorphous catalyst to produce cracked products. With the development of zeolite-based cracking catalysts, and short contact-time reactors, the FCC process has been able to crack progressively heavier feeds. Many FCC units now process feeds containing significant amounts of non-distillable or residual materials. These heavy feeds can be profitably cracked, but tend to have a high metal content, usually Fe, Ni and V. The Ni and V are considered poisons in the FCC process, which operates in the absence of added hydrogen. Excessive metals deposition on the catalyst causes production of excessive amounts of coke and large amounts of hydrogen.
Refiners have developed several ways to cope with high-metals feeds. Some refiners deasphalt the feed to remove the worst of the metal-containing components of the crude. Some refiners hydrotreat the feed, which deposits significant amounts of feed metals on the hydrotreating catalyst, thus protecting the FCC catalyst. One promising approach is metals passivation, addition of some element or compound which "passivates" or restrains the catalytic activity of metals deposited on the FCC catalyst.
U.S. Pat. No. 3,711,422 to Johnson, discloses adding antimony to an FCC unit to passivate metals in the feed. Many refiners are reluctant to add metals to their FCC units. Addition of metals such as Sb significantly increases the cost of the operation and creates the potential for adverse environmental impact. The added passivating metal must eventually go somewhere, either on the FCC catalyst, or perhaps deposited on the metal walls of the FCC unit.
A somewhat different approach to metals management in FCC units is the magnetic catalyst separation process recently developed and commercialized by the M W Kellogg Technology Company. This process removes a slipstream of circulating equilibrium catalyst (ECat), on the order of 10-40 tons/day, and processes this in a magnetic separation device which resolves the ECat into a high-metals fraction (which is discarded) and a lower-metals fraction which can be recycled to the FCC unit. Some details of the magnetic separation process may be found in one or more of the following patents: U.S. Pat. No. 4,406,773 to Hettinger, Jr. et al.; U.S. Pat. No. Re. 35,046 to Hettinger, Jr. et al.; U.S. Pat. No. 5,147,527 to Hettinger, Jr. et al.; U.S. Pat. No. 5,171,424 to Hettinger; U.S. Pat. No. 5,190,635 to Hettinger; U.S. Pat. No. 5,198,098 to Hettinger, Jr.; U.S. Pat. No. 5,230,869 to Hettinger et al.; U.S. Pat. No. 5,328,594 to Hettinger; U.S. Pat. No. 5,364,827 to Hettinger et al.; U.S. Pat. No. 5,393,412 to Hettinger; and U.S. Pat. No. 5,538,624 to Hettinger; all of which are hereby incorporated by reference.
It is widely known that magnetic separation can be used to remove a high-metals catalyst from lower-metals catalyst. This separation can be effected using batch or continuous processing, with the catalyst suspended in air, liquid, or disposed on a moving belt.